1. Field of the Invention
The present invention relates to a disk on which a servo pattern to compensate for head tracking is formed at the predetermined location on the track such as a magnetic disk and particularly to a disk on which signals are never switched between track pitches and an arithmetic processing method for servo pattern read from the disk.
2. Description of the Related Art
In a high capacity flexible magnetic disk and a hard disk, a servo pattern to compensate for tracking of a magnetic head is formed on tracks on its recording surface.
FIG. 6 illustrates a recording surface of a disk, while FIG. 7 illustrates an enlarged example of the servo pattern recorded on the tracks of the recording surface. On the recording surface of the disk, the tracks T are concentrically set and a servo pattern which is continuous on the radius line R of the disk is formed in a plurality of areas.
In FIG. 7, the track center of each track 1, 2, 3, . . . is indicated by a chain line Tc. Tp indicates the distance (track pitch) between the neighboring track centers. The scanning direction of the magnetic head H for reproduction is defined in the right direction in the figure and track width Tw of the magnetic head for reproduction is narrower than the track pitch Tp.
In the servo pattern a preamble (Sync) and an address mark (AM) are recorded first. The preamble and address mark are signals continuous without any switching in the radius direction of a disk crossing each track. The preamble is the signal in which single frequency is continuous toward the head scanning direction and when the magnetic head reproduces this signal, an amplifier gain of the reproducing circuit is fixed (AGC lock). Moreover, timing of the signal reproduction is set, for example, by locking of the PLL circuit with the preamble. Moreover, timing until the next address signal can be set by reproduction of the address mark explained above.
In the address signal, an address value such as track number (track No-) is recorded and this address signal is recorded within a constant width Aw in both sides of the track center Tc. This address signal can express an address value with a plurality of bits. The address signal is different for each track 1, 2, 3, . . . and the width Aw has the width interval equal to that of the track pitch Tp and the address signal is switched at the center between the track centers Tc.
Following the address signal, the A burst signal and B burst signal are recorded as the tracking signals. These A burst signal and B burst signal are recorded sandwiching the track center to have a time difference in the head scanning direction. The A burst signal and B burst signal are recorded in the equal amplitude intensity and are repetitive signals of the single frequency.
In the seek operation, whether the magnetic head H for reproduction has reached the target track or not is determined by reading the address signal. Moreover, when the magnetic head H for reproduction is scanning on the track, a servo gain is fixed by reading the preamble, moreover the single frequency signal of preamble is sampled to become the reference clock and thereby the address signal is read and the A burst signal and B burst signal are read. The tracking control is performed so that the center of track width Tw of the magnetic head H for reproduction is matched with the track center Tc by comparison between the reproduced intensity of the A burst signal and B burst signal read through timing difference.
In the servo pattern of the related art as illustrated in FIG. 7, the A burst signal and B burst signal are recorded to be switched defining the track center Tc as the boundary. Meanwhile, the address signal is the same signal in the width Aw defining the track center Tc as the center thereof and this address signal is recorded to be switched at the center of the track centers Tc.
Therefore, for the recording of servo pattern illustrated in FIG. 7, it is required to continuously write each signal for each half track pitch (Tp/2). Namely, the address signal 1-a and A burst signal A1 are recorded in the width of Tp/2. Next, the magnetic head for recording is fed for half track pitch (Tp/2) in the radius direction to record the address signal 2-a and A burst signal A2. This process is performed sequentially. The address signals 2-a and 2-b are same signals. Moreover, 3-a and 3-b, 4-a and 4-b, 5-a and 5-b are same signals, respectively.
When the track centers Tc are concentric on the recording surface of disk, following operation is necessary. That is, recording is performed for one circumference using the magnetic head for recording, the magnetic head for recording is fed only for half track pitch (Tp/2) in the radius direction during a turn of the disk, recording is performed during the next turn and moreover the magnetic head is fed for half track pitch (Tp/2) during the next turn of disk. As a result, the disk must be rotated for four turns in order to complete the recording of servo pattern in regard to one track center Tc.
Therefore, a certain time is required until recording of all servo patterns is completed on the recording surface of disk. Particularly, in the case of a disk aiming at larger capacity, the track pitch Tp is rather short and many tracks are formed. Therefore, much more time is required in the recording method which requires the time for four turns of disk to record the servo pattern of one track as explained above.
In addition, in the case when it is attempted to record the servo pattern illustrated in FIG. 7 during formation of spiral track center Tc on the recording surface of disk, signal must be recorded for half track pitch (Tp/2) respectively in both sides of the spiral track. Therefore, it is impossible that the magnetic head is scanned continuously along the spiral locus to record all servo patterns with only one spiral locus. Namely, the operation to write without any gap two kinds of different signals along the spiral locus is required but such recording is substantially impossible.
The present invention has been proposed to solve the problems of the related art and it is therefore an object of the present invention to provide a disk which can complete the recording of servo pattern with the minimum rotation thereof and allows recording of servo pattern enabling formation of track of spiral locus and also provide an arithmetic processing method for the servo pattern read from the disk.
The present invention is characterized in that the servo patterns are formed without any switching of signal in the track crossing direction between track centers in the disk where servo patterns are continuously formed in the track crossing direction at the predetermined positions of the recording surface of disk and this servo pattern includes an address signal which is switched at the track center defined as the boundary, an address identifying signal which is switched at the track center defined as the boundary, an even number/odd number detecting signal for identifying the even number and odd number of the track number of each track and a tracking signal which is recorded in different conditions in both sides of the track center.
The address signal and address identifying signal are switched, for example, for every two tracks. In this case, both address signal and address identifying signal are switched, defining different track centers as the boundaries.
The tracking signal is composed, as illustrated in FIG. 1 and FIG. 2, of the A burst signal and B burst signal recorded in the position which are different in the timing defining the track center as the boundaries. Alternatively, it is also possible that the signals of different frequencies are recorded on the same position in timing in both sides of the track center.
In the present invention explained above, the signal of the same width as the track pitch Tp is recorded, for example, by the over-writing which may be attained by utilizing the magnetic head for recording having the track width which is a little larger than the track pitch Tp.
Therefore, on the occasion of recording the servo pattern matching with the concentric tracks, it is enough for magnetic head to be set to one track pitch as the feeding thereof in. the disk radius direction (track crossing direction) and recording of all servo patterns can be completed within the time equal to a half of the time required in the related art.
Moreover, on the occasion of setting the spiral track center, recording of all servo patterns can be completed by the single spiral scanning of the magnetic head for recording.
The address signal explained above is a gray code in which only one bit is different between the neighboring address signals and it is preferable that only the lest significant bit is different between the neighboring address signals. Moreover, it is also preferable that the address identifying signal is the signal of one bit or more in which the phase is changed in every two tracks.
When the gray code is used as the address signal explained above, a recognition error of an address can be set to one bit (lest significant bit in the binary value) and an error correction can be done easily even when the address is read erroneously. Particularly, in the present invention, since the address signal is switched defining the track center as the boundary, if the reproduction head is in the ON track condition, it is never freed from interference of different address signal in the neighboring track, resulting in probability for generation of erroneous detection of address value. Therefore, when the gray code is used as the address signal, error correction can be done easily at the time of arithmetic operation of address. This address signal is changed in every two tracks by defining, for example, the even number tracks as the boundaries.
Moreover, the address identifying signal is changed, for example, in every two tracks defining the track center which different from that of the address signal as the boundaries and its phase is also switched between the neighboring signals. The address identifying signal is changed, for example, defining the even number track as the boundary. Using this address identifying signal, the even or odd number truth value of the address value (address No.) indicated by the address signal can be identified. Since this address identifying signal is the shortest signal expressed by at least one bit of the binary signal, the recording space of this address identifying signal may be very narrow.
In the present invention, it is allowed that the address signal changes defining the even number track as the boundary and the address identifying signal changes defining the odd number track as the boundary.
Moreover, the even number/odd number detecting signal changes its phase in every two tracks and this signal is formed in such a manner that an amplitude of the reproduced signal is varied by interference of a couple of signals when the head scans the track center as the boundary of signals of different phases. For example, the even number/odd number detecting signal has the phase which is different by 180 degrees by defining the odd number track center as the boundary.
When the even number/odd number detecting signal is used, a class of following tracking signal can be determined easily.
Next, the servo pattern arithmetic processing method of the present invention is characterized in that the servo pattern recorded on the disk is reproduced to determine, on the basis of the reproduced output of the even number/odd number detecting signal, whether it is probable or not that erroneous detection of the address value is generated due to the interference of different address signals which are neighboring by defining the reproduced track as the boundary. When it is determined that it is probable that erroneous detection is executed, erroneously detected address value is corrected on the basis of the reproduced output of the address identifying signal.
For example, when even number or odd number of address value to be detected is identified by referring to the reproduced output of the address identifying signal and the address value which is probably detected erroneously due to the interference between the address signals is even number, the least significant bit of the address value after the address signal is binary-converted is set to xe2x80x9c0xe2x80x9d and when the address value which is probably detected erroneously due to the interface between the address signals is odd number, a correction is conducted so that xe2x80x9c1xe2x80x9d is subtracted from the address value after the address signal is binary-converted and the least significant bit is set to xe2x80x9c1xe2x80x9d.
Moreover, when it is determined that the even No. track is reproduced from the reproduced output of the even number/odd number detecting signal, the track number can be calculated by doubling the address value obtained from the address value and when it is determined that the odd No. track is reproduced, the track number can be calculated by doubling the address value obtained from the address signal and adding 1 thereto.
In the present invention, when the even No. track of the disk is reproduced, the address No. can be calculated by doubling the address No. of the binary value converted from the address signal and when the odd No. track is reproduced, the address No. can be calculated by doubling the binary value converted from the address signal and then adding xe2x80x9c1xe2x80x9d thereto.
With such simplified arithmetic process, the track which is scanned by the magnetic head for reproduction can be identified easily.
Moreover, in the track where address signal changes by defining the track center as the boundary, the track No. cannot be read accurately due to the interference of address signal but interference by the address signal can be recognized by making reference to the even number/odd number detecting signal and it can be detected accurately whether or not the error correction of address value is necessary.
In addition, when it is determined as a result of reference to the even number/odd number detecting signal that the address signal is probably interfering, following error correction is performed.
That is, when different address signal is reproducing the neighboring track, it is required to refer to the address identifying signal. When the address signal which changes by defining the track center as the boundary sequentially becomes even and odd numbers with increase of the address value (when the truth value is even No.) as a insult of identification by this address identifying signal, the correction is made so that the least significant bit becomes xe2x80x9c0xe2x80x9d after the address value is converted to the binary value and when the address signal sequentially becomes even and odd numbers with increase of the address value (when the truth value is odd number), such address signal is converted to the binary value and thereafter xe2x80x9c1xe2x80x9d is subtracted to correct the least significant bit to In this error correction, an error as a result of interference by different address signal can surely be corrected. It is because only one bit of the address signal recorded by the gray code is changed between the neighboring address signals and when the address signal is converted to the binary value, a change of one bit explained above corresponds to the least significant bit. Therefore, when the truth value of the address value (address No.) can be found as the even No. or odd No., correction can be realized by processing the least significant bit as explained above. This address No. can be identified as the even No. or odd No. from the address identifying signal. When the address signal and address identifying signal which are changing in every two tracks as explained above change alternately by defining different track centers as the boundaries, if the address signal results in interference on the track, the address identifying signal does not result in any interference. When the address signal does not result in any interference, the address identifying signal results in interference. Thereby, the truth value of the address No. can be identified easily as the even number or the odd number.
The address identifying used for error correction is enough when it can identify xe2x80x9c1xe2x80x9d and xe2x80x9c0xe2x80x9d and one bit signal maybe used. Therefore, many correction bits to perform the desired bit error correction and its complicated arithmetic processes are unnecessary.
Moreover, the servo pattern arithmetic processing method of the present invention is characterized in that tracking control direction can be recognized on the basis of the even number/odd number detecting signal when the tracking signal recorded on the disk is reproduced.
In the present invention, since the tracking signal (for example, A burst signal and B burst signal) is recorded without switching between the track centers, it is impossible to avoid interference of the address signal and it is impossible to detect polarity (direction) of the tracking signal only from the address signal. Therefore, direction of tracking control is determined using the even number/odd number detecting signal.